How do I use -기, -는 것, -(으)ㄴ+ noun, -(으)ㄹ + noun?
So I am learning about turning verbs into noun form with -기& -는 것. These are still difficult for me as to why a verb would need to be used as a noun. From the material I am using it says it has the meaning of "the act of doing something" or verb ending "-ing". But isn't that what -고 있어요 is for? Even more confusing are the other two noun groups/. The past tense -(으)ㄴ+ noun&the; future tense noun group -(으)ㄹ + noun. When going through examples, this all seems confusing as to me it seems that saying 아/어/였어요 or (으)ㄹ 거예요. Is this right or am I understanding this wrong? Can someone please explain this to me better&maybe; help me understand when to use which or why one way should be used over another. I feel there is more to this that what is being presented to me.
Sample sentences show 제가 보는 책이에요, 제가 본 책이에요,&제가 볼 책이에요.